This invention relates to implantable devices which detect and/or treat tachyarrhythmias (rapid heart rhythms), and more specifically, to mechanisms for monitoring the rhythm of the patient's heart and for monitoring the operation of the device.
In conjunction with monitoring the operation of an implantable device and the condition of the patient in whom the device is implanted, it has become common for the implanted device to keep records of and counts of events occurring during operation of the device. For example, as disclosed in U.S. Pat. No. 4,557,266 issued to Schober et al, the events counted may be as simple as delivered atrial and ventricular pacing pulses, sensed atrial and ventricular depolarizations, detected premature atrial and ventricular depolarizations and runs of premature depolarizations. In the context of implantable antitachyarrhythmia devices, it is common to maintain counts of the occurrences of the various arrhythmias detected by the device and counts of the various types of therapies employed by the device. It has also become common to retain measured parameters associated with operation of the devices, such as R-wave and P-wave amplitudes, battery voltage, lead impedance and the like, and in some cases to store information with regard to such parameters in the form of trend lines illustrating the values of the parameters over time, as disclosed in U.S. Pat. No. 5,088,488, issued to Markowitz et al.
These stored counts and/or measured parameters are typically provided to the physician during interrogation of the implanted device using an external programmer. In such cases, the implanted device uplinks the various stored counts and measured parameters since the last time the device memory was cleared. In some such devices, the various counts and/or stored parameters may be cleared by the physician in conjunction with interrogation of the device, so that upon subsequent interrogation, only the events occurring and values measured since the previous interrogation will be reflected in the stored information. This approach, however, results in the loss of the ability of the device to retain counts or values taken over an extended period of time, spanning multiple interrogation sessions. An additional alternative has been to employ time stamps in conjunction with the recording of the events occurring and parameters measured by the implantable device, so that the physician can determine, by comparing the time stamps to the time of the previous interrogation, which events occurred subsequent to the previous interrogation session.